1. Field of the Invention
This invention relates to an enhanced method and device for detecting molecules, and more specifically, this invention relates to a method and device for detecting the presence of molecules through the manipulation of structural factors which effect dimerization of recombinant antibody variable domains.
2. Background of the Invention
Animals make antibodies in response to the introduction of microscopic substances which are foreign to the host. The antibodies bind these substances and after such attachment, the resulting larger complex is either deactivated or else detected and expelled from the host.
Conventional antibody molecules are used in a wide variety of applications, including detection and diagnostic systems, assays, and treatment protocols. Currently, antibodies are manufactured in the form of polyclonal antisera by immunizing animals and subsequent collection of sera. Antibody proteins also are produced as monoclonal antibodies by lymphocyte/plasma cell culture or as recombinant antibody molecules in bacteria or other cells.
However, all of these various methods are somewhat costly and time consuming. The use of intact antibodies in the above-mentioned detection scenarios has been replaced in part by the use of antibody fragments such as the antigen binding fragment (Fab), which contains the variable heavy domain (VH), one variable light chain (VL) and one constant domain from each chain. Parts of the Fab also have been utilized, including for example, the variable fragment Fv, which consists of VH and VL in combination. To date, the Fv has been the smallest functional antibody construct utilized.
There are drawbacks to the use of recombinant antibody fragments in these methods, however. For example, Fv constructs tend to be unstable as VH and VL can dissociate from each other, with the VH precipitating. Also, Fv molecules have only one binding site and are thus monovalent, as opposed to intact antibodies, which are bivalent. As a result of this monovalency, detection sensitivities decrease significantly. Further, the single valence makes Fv molecules unable to cross-link molecules to which they bind. Cross-linkage is important in various medical and biotechnological applications. Substantial effort has gone into constructing linked or bivalent Fvs. See, for example, Hudson P., (1998) Curr Opin. Biotech. 9, 395-403. However, with this substantial effort comes higher implementation costs.
Another disadvantage of current methods is that costs associated with recombinant antibody production are high and reflect the generally low yields of production. Specifically, high production costs of Fv molecules are attributed to the required expression of two genes or the two-gene equivalent as well as the use of artificial polypeptide linkers to connect domains.
A need exists in the art for detecting molecules (e.g. ligands or antigens) with recombinant antibody fragments which, like intact antibodies, are multivalent. The individual detector modules also should be more economical to produce than current detectors.